Optical fiber communication is a rapidly developing and maturing technology. Currently, optical fiber technology is being implemented in local area networks, long distance terrestrial systems and even longer distance submarine systems. As the area serviced by these communication systems expands, the number of fiber connections is also increasing, thus creating the need for improved fiber connections and couplers having low loss and minimal distortion. It is especially desirable to attain a maximum coupling eficiency of light from transmitters, such as semiconductor lasers, to microlensed fibers and from the microlensed fibers to detectors. For example, see the article by G. Wenke and Y. Zhu entitled "Comparison Efficiency and Feedback Characteristics of Techniques for Coupling Semiconductor Lasers to Single-Mode Fibers" in Applied Optics, Vol. 22, No. 23, Dec. 1, 1983, pages 3837-3844.
Small lenses with relatively high coupling efficiency may be prepared by forming a tapered fiber and heating the end of the taper, for example, with an electric arc. Etched tapered fibers are prepared by etching off the cladding from an end portion of a fiber with buffered HF resulting in a taper and subsequently forming the small lens at the end of the taper. Drawn tapered fibers are prepared by simultaneous drawing and heating of a section of a fiber in an electric arc. The length of the tapered region can be controlled by the amount of heating and by the drawing speed. After the constricted portion is melted off, electrode arc heating produces a microlens at the end of the tapered fiber. In some cases, the microlens is produced by dipping the end of the tapered fiber into a melt of high-index glass. An article by K. Mathyssek, J. Wittman and R. Keil entitled "Fabrication and Investigation of Drawn Fiber Tapers with Spherical Microlenses" in Journal of Optical Communications, Vol. 6 (Dec. 1985) 4, pp. 142-146, as well as U.S. Pat. No. 4,565,558 issued on Jan. 21, 1989 to R. Keil et al. and U.S. Pat. No. 4,589,897 issued on May 20, 1986 to K. Mathyssek et al., discusses drawn tapered fibers with microlenses.
However, while such lenses may possess relatively high coupling efficiency, these two processes do not lead to truly reproducible results due to a number of production inefficiencies. Among the inefficiencies are the wear of arc electrodes as the period of their use increases and a difficulty in forming lenses on certain fibers which may not be symmetrical. An example of such a fiber could be a so-called D-fiber in which a segment of the cladding is removed on one side of the fiber. Another example could be a polarization preserving fibers for which microlens formation presently is difficult if not impossible.
It is, thus, still desirable to fabricate microlenses on the optical fibers in an efficient and a controllably reproducible manner.